I first noticed these flowers last year. They grow along an alley that I sometimes follow on my walk to and from work. They are the earliest blooming flowers that I see in my neighborhood; my hyacinths and tulips haven’t even pushed a shoot out of the ground.
On Thursday (March 20th, the vernal equinox in the northern hemisphere), none of the flower buds were open.
Eranthis hyemalis (winter aconite) flower buds
On Friday, several flowers were open.
Eranthis hyemalis (winter aconite) flower
An internet search revealed that these are Eranthus hyemalis, commonly known as winter aconite. They are a member of the buttercup family (Ranunculaceae) and are native to Europe.
If you decide to plant very early blooming flowers like these, my advice is to plant them in areas where you’re likely to see them (and smell them, if you plant something like hyacinths). You’re probably not going to spend a lot of time outside when it’s cold, windy, or rainy as it often is in the spring, so consider planting them near the entrance to your house or garage.
I posted more photos of spring flowers last year.
gardenblog2013 
Are these buttercups? Pretty!